X-ray tube structure



p 2, 5 J. P. LANEFSKI 2,850,656

X-RAY TUBE STRUCTURE Filed Sept. 21, 1954 2 Sheets-Sheet 1 INVENTOR JOHNP. LANEFSKI l8 Flez BY g qgg ATTORNEY Sept. 2, 1958 J. P. LANEFSKI X-RAYTUBE STRUCTURE 2 Sheets-Sheet 2 Filed Sept. 21, 1954 FIG.3

INVENTOR.

JOHN P. LANEFSKI TORNEY States X-RAY TUBE STRUCTURE ApplicationSeptember 21, 1954, Serial No. 457,348

3 Claims. (Cl. 313-59) This invention relates to a novel X-ray permeablewindow for use in X-ray tubes. More specifically, this invention relatesto an X-ray window which is bowed or corrugated in such a manner that itis able to change its shape in order to compensate differentialexpansion.

A high rate of failure of beryllium windows in certain types of X-raytubes has been observed for some time. It has been found that changes intube geometry will sometimes prevent destruction of the windows.However, changes in geometry also change characertistics in manyinstances, and often characteristics of the modified design are lessdesirable than those of the original.

My observations indicate that the principal cause of destruction ofberyllium windows is the sudden, severe heating produced by bombardmentof the windows by secondary electrons. More specifically, it is thenonuniform heating of various regions in the window and its supportwhich results in the destruction. Beryllium is a material which has arelatively high expansion coefiicient and relatively low thermalconductivity. Consequently, regions removed from parts of the berylliumwindow which are heated by bombardment tend to become heated relativelyslowly so that upon beginning tube operations extreme differences areencountered in the temperature of different regions in the window. Infact, it is possible for secondary electrons to generate a high surfacetemperature on the inside surface of the beryllium window while the restof the window, including the outer surface, remains relatively cool fora period long enough for undesirable expansion effects to occur. Sincethe windows are rigidly fixed to the envelope structure in order tocomplete the vacuum envelope, the differential expansion which resultswill inevitably cause high internal stresses and possible deformation.If such is the case, the repetition of straining and relieving thestrains during a period of use will cause cracks and fissures in thewindow and a consequent loss of vacuum.

My invention permits the relief of expansion-produced strains so thatthey will not cause window destruction. My invention permitsadjustability in the window structure itself so that expansion effectsmay be relieved despite the fact that the window is rigidly affixed atall its edges to the relatively massive envelope structure. Thisadjustability is provided by shaping the window itself in such a mannerthat its expansion will merely exaggerate the shape which has alreadybeen provided in the window. Ordinarily, in accomplishing this end, thewindown is convoluted in the same general pattern as the supportedperiphery of the window structure. For instance, when employing theinvention with a conventional round disk window, the pattern of theconvolution is circular wherein the circles are concentric with junctionof the window and the support structure. In its simplest form, such around window is providedwith a single slight bow in one direction or theother, but preferably extending away from the target. Despite therelative rigidity of its support at its periphery, which rigid supportprevents outward expansion, such a w1ndow when atent G heated is able toabsorb its expansion by increasing the gradient of the slopes of theconvoluted or bowed part of the window. Thus, strains which wouldotherwise be produced by expansion are relieved without damaging thewindow structure.

For a better understanding of the present invention reference is made tothe following drawings:

Fig. 1 illustrates in partial section an electron tube wherein oneversion of the present invention is employed;

Fig. 2 illustrates in cross-section a window construction of the presentinvention;

Fig. 3 illustrates schematically and in section an apparatus for formingthe window structure shown in Fig. 2.

Referring to Fig. 1 an X-ray tube is illustrated wherein part of thevacuum envelope 10 is composed of a metal casing. The remainder of theenvelope may be composed of glass or other suitable dielectric materialthrough which leads from the cathode are brought out. Within the vacuumenvelope are cathode 11 and anode 12. The cathode filament is notillustrated but is enclosed within the shielding and focusing memberwhich is illustrated in elevation. The anode is a heavy copper blockwhich, in this case, is kept at ground potential by directly coupling itto the envelope 10. Within the envelope the active surface of the anodeis provided by a target block 13 of tungsten or other suitable densematerial. The filament within focusing member 11 produces an electronfocal spot on target 13. From this focal spot, in turn, originate X-rayswhich leave the vacuum envelope through beryllium window 14 in the endof the structure. Unfortunately, in addition to the X- rays, high energysecondary electrons are emitted from the target and impinge theberyllium window. These high energy electrons cause severe heating ofthe window and repetition of this heating in a conventional window mayproduce a recurrence of trains which will eventually cause breakage ofthe window. The window 14 is mounted in a pair of annular bezel members15 which are fixed securely and vacuum tight to the metallic casing ofvacuum envelope 10.

A casing 17 is provided to slip over the envelope portion 10. The spacebetween the casing 17 and the envelope member is filled with insulatingoil. Member 17 also provides a socket for connection to a terminal 19 onthe end of cable 18. This terminal 19 may be partially viewed in Fig. l,but, for the most part, it extends inwardly into the socket provided forit in member 17.

As may be seen in Fig. 2, the X-ray permeable window 14 in accordancewith this invention is provided with a slight convolution or bow inorder to give it flexibility. This convolution or bow is locatedconcentrically with the supported periphery of the window. Since thewindow 14 is located directly in the path of X-rays produced at target13 and also in the path of secondary electrons, it is subjected to rapidheating to which its supporting structure is not subjected. This heatingtends to produce expansion which, were no provision made to accommodateit,.would result in the build up of internal strains within the windowstructure. However, with the structure of the present inventionexpansion produces an increased bowing of window 14. In other words, thegradient of the bow increases or becomes exaggerated so that expansionis easily compensated.

An alternative construction of the window would be to make it corrugatedwith any number of convolutions arranged concentrically with the supportfor the window. The term convoluted shape is intended to include asingle bow or multiple convolutions in a window.

The beryllium or other X-ray-permeable material may be formed into awindow for use in accordance with this invention by the apparatus shownin Fig. 3. This apparatus is meant to be representative only and manyother Patented Sept. 2, 1958 against platform .22 in such a manner thatthe bell jar maybeevacuated or -filled with a non-oxidizing gas.-Advantageously, the. structure basically consists of a pair ofv jawsgenerally designated 23 and Y24 between which the beryllium disk'25 tobe formed is placed. Thejaws are the heating elements of a resistanceheating system 7 which consis ts. of copper block members 27 and'28,stainless steel die members 29 and 30 and refractory memhers 31 and 32,of such material as graphite. The bottom copper block is made to fit abase piece 34 which holds it securely in place. The upper block 27 isurged downwardly' by spring member 35. 7 Electrical connections (notshown) :are employed to provide a current through the forming assembly.a

In operation of the assembly shown in Fig. 3 the region under the vacuumjar 21 is evacuated or filled with nonoxidizing atmosphere. Block 23 isacted upon by spring 35 and presses downward against disk 25 which iturges toward block 24. The spring pressure of spring 35 is sufiicient tourge the blocks into good electrical contact with disk 25 but notsuflicient to deform the disk while cold. Current is then permitted toflow through the block. Because of the resistance encountered inrefractory material 31 and 32, the die pieces 29 and 30 are heated andthe heat is conducted to disk member 25. The heating is sufficient tosoften the disk which then deformsunder the urging of spring 35 into theshape provided by the die members 29 and 30. Inasmuch as pressure isretained on this disk until it is cool, the disk will retain the formedshape, as illustrated in Fig. 2, and may be employed in a tube assemblyin accordance with the present'inv'ention.

' Die members of various shapes may be employed in order to obtainwindows of shapes difierent from that illustrated in Fig. 2. Otherchanges in the apparatus and the geometry of the window illustrated willoccur to those skilled in the art. All such changes or modificationsWithin the scope of the claims are intended to be within the scope andspirit of the present invention.

I claim:

1. An X-ray tube embodying an elongated housing containing a cathode andan anode and having in one end thereof an opening for exit of X-raysfrom the; anode, and within the opening a window formed of materialhaving expansion characteristics different from those of the material ofthe housing adjacent the opening, the

window being of a metal relatively easily penetrated by X-rays and ofrelatively inflexible characteristics, the window further being arelatively rigid disclike member lying in a plane normal to thelongitudinal axis of the. housing and having an annular. marginal,portion lying in said plane and vacuum-sealed throughout its peripheryto the inner wallofthe opening, and further having its central portionintegral with the annular marginal portion and formed with an outwardlybowed convolution whereby the central portion of the relatively rigidwindow may expand freely with respect to the housing.

2. An X-ray tube substantially as set forth in claim 1 wherein thewindow is beryllium.

3. An X-ray tube embodying a cylindrical housing containing a cathodeand an anode and having in one end thereof a substantially circularopening for exit of X-rays from the anode, within the opening arelatively thick and rigid beryllium window having expansioncharacteristics different from those of the material of the housing, I

and an annular bezel vacuum-sealed throughout its periphery to the innerwall ofthe opening and having a groove formed in its inner peripheraledge, the window being a disclike member having a substantially planarannular marginal portion which is positioned within and vacuumsealed inthe groove inthe bezel and further having its central portion integralwith the annular marginal portionformed with an outwardly cupped shapewhereby the central portion of the relatively rigid window may expandfreely and unrestrictedly with respect to its supporting'structure. V

References Cited in 'the file of this patent Atlee Jan. 10, 1956 M rea-r

